In data storage devices, data is typically stored in tracks on a medium. To access the data, a head is positioned within a track while the medium moves beneath the head.
In many data storage devices, the head is positioned by an actuator assembly that includes a motor that rotates one or more actuator arms. Each actuator arm supports a suspension that in turn supports a head/gimbal assembly. Typically, the suspension includes three distinct areas: a base plate area that connects to the actuator arm, a spring area that provides a vertical spring force to bias the head toward the medium, and a load beam that extends from the spring area to the head/gimbal assembly. The spring force provided by the suspension is designed to allow the head to follow height variations on the surface of the medium without impacting the medium or moving too far away from the medium.
In the past, suspensions have typically been formed from sheets of stainless steel. Stainless steel is used because it provides the desired spring force for the head, it has mechanical properties that are relatively insensitive to heat, it does not outgas, and it can be welded to other parts of the actuator assembly.
In some prior art systems, using sheets of stainless steel results in a suspension in which the spring area and the load beam are the same thickness. Because of this, both areas exhibit similar mechanical properties. However, because the spring area and the load beam perform different functions, it is desirable that they have different mechanical properties. In particular, it is desirable that the spring area be more elastic or flexible than the load beam because a load beam that is too elastic will tend to bend and resonate in response to windage induced forces.
To solve this problem, the prior art has developed several techniques for forming a suspension so that the thickness of the spring area is less than the thickness of the load beam. In one technique, the spring area is partially etched to reduce its thickness. However, partial etching provides poor thickness control of the partially etched portions and results in poor pre-load stability in the spring area. A second technique welds a second metal sheet to the load beam. However, welding is costly and causes distortion of the load beam due to the heating of the metal. In addition, welding requires a minimum surface area that will not be present in smaller suspensions of the future.
A third technique taught by the art is to form the suspension through lamination. For example, U.S. Pat. No. 4,996,623 shows a suspension in which the load beam is formed with a polyimide layer sandwiched between a copper layer and a stainless steel layer. In the '623 patent, the copper layer and stainless steel layer are bonded to the polyimide using an adhesive such as a polyimide-based liquid adhesive.
Although laminated structures of the past help dampen some oscillations in the suspension, the use of two layers of metal in the laminate is undesirable because of the relatively low stiffness to mass ratio of most metals.
The present invention provides a solution to these and other problems, and offers other advantages over the prior art.